Method and apparatus for balancing rotors



May 25, 1948. F. w. MEREDITH ETAL I METHOD AND APPARATUS FOR BALANCING ROTOBS Filed March 1, 1944 5 sheets-esheet 1 Z'Nve NToR May 25, 1948. I F. w. MEREDITH ETAL 2,442,308

METHOD AND APPARATUS FOR BALANCING ROTORS Filed March 1, 1944 5 Sheets-Sheet 2 vqanmmv- -8. M 60% ,MY

May 25, 1948. F. w. MEREDITH ETAL 2,442,303

METHOD AND APPARATUS FOR BALANCING ROTORS Filed March 1, 1944 5 Sheets-Sheet 3 I INVfiA/To/Q a. w, M4411 2,13. m

B} lsuj cve MYW y 1948- F. MEREDITH ETAL ,308

METHOD AND APPARATUSFOR BALANCING ROTORS Filed March 1, 1944 5 Sheets-Sheet 4 J ryveAn-og S. Mm 6,9110% May 25, 1948. F. w. MEREDITH ETAL 2,442,303

METHOD AND APPARATUS FOR BALANCING Ro'rORs I 5 Sheet-Sheet 5 FiledMarch 1, 1944 win i e, mvwdzam INugA/TO Patented May 25, 1948 METHOD AND APPARATUS FOR BALANCING ROTORS Frederick Wiliiam Meredith, Eric Beecroft Moss, and Hubert Edward Whatley, Cricklewood, London, England, assignors to S. Smith & Sons (England) Limited, a British company Application March 1, 1944, Serial No. 524,652 In Great Britain October 19, 1943 11 Claims.

This invention relates to balanced rotors and particularly to rotors employed for gyroscopic apparatus, such as artificial horizons for aircraft and has for an object to provide a simple and accurate method of producing a rotor which is dynamically balanced.

According to this invention, there is provided a rotor which has been balanced by successively applying unbalancing forces of similar value and sense on opposite sides of the spin axis of the rotor, by rotating the rotor through a given range of speed and comparing the out-of-balance reactions set up by the rotor at a given speed after each unbalancing force has been applied, by removing and/or adding material from or to the rotor at the points of application of the unbalancing forces and by again comparing the reaction and if necessary removing and adding material until the resulting out-of-balance reactions are the same. Preferably, two such balancing operations are carried out, one by applying successively unbalancing forces to two points on opposite sides of the spin axis on a line passing through that axis and the second by successively applying unbalancing forces to two other points of the rotor on a line transverse to the first said line and passing through the axis. By arranging the two lines to be at right-angles to one another balancing about one axis can be effected without influencing the balance about the other axis at right-angles thereto. Balancin is thus effected first in the plane of one face of the rotor and is then repeated in respect of the other face.

Unbalancing forces of similar value are preferably obtained by so arranging said points as to be disposed at equal distances from the axis of spin and by applying equal loads successively to these points. For example, the loading may be effected by applying a mass successively to points on a side face of the rotor.

The invention includes Within its scope a method of balancing a rotor which consists in dynamically balancing the rotor about each of two axes at right-angles to one another and to the axis of spin.

The out-of-balance reactions may be measured by recording the extent of deflection of the mounting for the rotor, which mounting may comprise a frame resiliently carried by a support so as to be movable in a direction transverse to the rotor axis. In such an arrangement, the rotor is rotated through a range of speeds including a speed corresponding to the natural period of vibration of the resiliently mounted system, whereby resonance of the frame is set up and under these conditions the amplitude of vibration is a measure of the out-of-balance reaction.

The frame may be arranged to oscillate about an axis at right-angles to that of the rotor.

In such an arrangement the axis of oscillation may be arranged in the plane of one face of the rotor while the aforesaid unbalancing forces are successively applied to points on the opposite face, the material being removed from and/or added to the latter face until the maximum deflection of the frame is the same for each application of the unbalancing force, whereafter the position of the rotor is reversed in the frame and a similar procedure is followed with'respect to the other face. Thus, complete balancing can be obtained of the rotor in two planes passing through the two faces.

The amplitude of vibration of the frame may be measured by arranging the frame to operate a magnetic pick-up which generates an electric current proportional to said amplitude and which pick-up is connected in circuit with an appropriate indicating or recording instrument. Preferably, filters are associated with the circuit so as to filter out any unwanted vibrations, such as those generated in the bearings and transmitted to the magnetic pick-up, or those generated by the mechanism driving the rotor. Preferably, the filtered vibrations set up by the resilient frame are amplified before being passed to the indicator.

As indicated above, the rotor requires to be rotated up to or slightly beyond the speed corresponding to the natural period of vibration of the resilient system; also, as indicated above, the driving mechanism of the rotor may set up vibrations. The periodicity of such vibrations will be proportional to the speed and will usually be within the audio-frequency range. This is particularly the case where a rotor is driven by an air jet impinging on buckets, or the like, on the periphery of the rotor, which results in. a high pitch whistle being generated, the frequency of which is proportional to the speed and number of buckets. The speed of the rotor may be automatically governed at, or just beyond, the speed corresponding to the frame resonance by providing means such as a microphone responsive to said Whistle so as to produce a current having a frequency proportional to the rotor speed, which current is passed through a circuit having a filter sharply tuned to the bucket or whistle frequency, and by. arranging the currentipassedby. the filter to operate a relay to out off the source of supply for driving the rotor.

The following is a description of one formrof apparatus suitable for balancing the rotor of a gyroscope, reference being made to the accompanying drawing, in which:

Figure 1 is a side elevation of the resiliently mounted frame for the rotor; rash-i a e:-

Figure 2 is a plan of the arrangement shown in Figure 1;

ment;

Figure 4 shows an electric circuit foramplifying the electrical impulses generated by a pick-up on the resiliently mounted-frame; Figure 5 shows an electric circuitffor. controlling the'speed' of rotorby means of a microphone responsive'to motorinoisesw-r Referring-to thearrangement shown-- in Figures :1 to 3,- the rotor -lismounted-in azframel which is-either=constitutedbysthe.ri-ngused for the-final gyro'assembly-or by aspecial frame; The ring or frame is clamped between suitably shaped plates 3* to whioh-- are-attachedthe leaf spring supports 4." riI-hese 'springsare. matched in stifiness; -viThe other ends-of, thespring supports are 'ligidly mounted ona-heavy base. 5' which-is-slung on heavywhelic-al prings 6 tron-some suitable structural member :(such: as. a rroof girder) toensurethat -the-system istimmu-ne from stray vibrations-fromvadiiacent maohinery yetca gramophoneppickmp Fl, which maytbe orthe -magnetic type, is-mountedi-on theheavy baseiand is 'conrrectediato the vibrating system as by the connecting 'pieoevfiui 1, Thenrotor istdriven byn-an air jet 8 which is swivel mounted at l-D on the base 5;; g

As will be seen from Figure lrltherotords arranged in the'f-rame so rthattheilower surface of =the rotor includes'the axis --l=l :aboritswhichdhe 1 frame vibrates; I so. I that 1 any outeof-balance .on this surface of the rotor-can have no-effectontthe iframe. -On 'the' othen surface. of;.the :rotor 'two pairs of index marks 2', 1-2 andil 3;; 132' areprovided; eachpai-r dying on-a line throughthe; spin Y axis but onopposite: sides thereof and equidistant therefromand the'twoelines being at right-angles -to one another; Asmall-pieceof putty St is then placed-ton one 01; the index marks and-the rotor -run'up' by an air-jet-to above resonance and the air cut-om Asth'e-speedfalls through resonance the indicator hereinafter described WiH-I'IISQ to a maxiinum reading and; this maximum reading is noted-.azlhe piece ofputtyisrthenputaonithevop- 'positeiindex-mark andthe rotor again runzup. :-As the speed once -more falls; through resonance the '2 maximum reading is againmoted; .',If two readings are-the same the topgurfacemf the rotor;is --halanced about-a line at:right"-angles to that passing through theyfirst said index-tmarksz" In -gen- =eral, however, therefwill be adifi'erence-between .the.. two readings indicating ia-n out-rof-balance. Ahole is drilled oncthe mark forrwhich thegreater readingwas. observed, and this .h 1e is pro r s- ."s'ively increased .-sl Ze -,until equal .re.adings.are obtained with 'the putty on the two sides. The

two marks at right-angles to the first two are Figure 3 is an end elevation of the arra gethen treated in a similar way to balance the top surface of the rotor about a second axis at rightangles to the first. Finally, the rotor is turned round and the other surface of the rotor is treated in an exactly similar manner.

As shown in Figure 4, the pick-up 1 is connected in circuit with an indicator l4. Thiscircuit comprise two electronic valves l5. 4 6-whicl1- are coupled by thetuned circuit I1 tuned 10 to couple the frequency of resonant vibration of the frame from the pickup.

This signal is passed to the amplifier, and areaches;the1grid;;0h;the valve I5 via the filter network 20, 2|, 22 and potentiometer sensitivity con- 5 trol l-9.

l'lhe filter network serves to filter out any un- -e-wantedehigh frequency components of the sig nal,- e.-g; due-to ball vibration and air turbulence. Potentiometer l9 controls the signal input to :the-valife lbgjnfour graded steps. The sensitivity of 'the' amplifier is selected in accordance with thedegree of balancing required.

The anode of the valve I5 is tuned by the resonance, circuit I Land the feed resistance is, de- 5.-c. llple'd by the condenser 23 connected with the earth linec Q j ,1, t The signaljis, passedon '13Q,l}h6'g1 id' 0f theelectronicvvalvenl 5. via the con'denser;2 4.- The signal produced in the-anode ci-rcuit ofthe valve 1 6 is passed. to the i d cator 1. .wh h* ;eQ t across; the hI1;0de-oathode circuit of the valve thronehthecond n r 5 1 In practice, trm y etd ficu t .tort l. en .ro tor v,has ,bejenrun upaboye resonai ce. 35.. if it happens thatthepieceof puttyexa tly be ances the rotor the e, ,wi. .be. no titr on ;o the frame. and consequent yth .ih l eator .wi l; h no resonance. :Lf lhe operator may the i hinh has. .notrun upv the rot r,s fh ient randiwil g0 40 on. increasingthe, speed. th rehy'w st ne. time:

e. To, overcome thisa microphone] 6 is arranged ,tOLpick;urilthebucket noise. an so generate a .currentthe ireq encyroilwh ch s p o o tional to rotor speedarldith c rre tf omth m sroph is. is passeri .throuehta. band-ne ts..filtera smht ..,.witl.1 athermioni re ay-sha ply ti e tn he 7 iquency or the. whistl -prom ted by the i st a ,rotor'.a th .xeso an ejfr 'quen y of he f am the relay voltagean mhl y being .snchthat filigrei y opmiat son; the shar lrr s ne rtiqnnf t characteristic of, theban -r a e' fi rt' T e re ;;istarrangedat c tof the supplyofa to the driving. .iet beyondl'e na q hp H The speedtof the roto'1"is eontr olled by a cry stal microphone, ,and associated circuit sh o wn in Elgure 5.:frhec ystarm crophQ e; 2.6 ns t ve to the whistle set up. by the driving jet for the rotor: I r Th c rcuitcornpri es ahieh. a n am l f e in 60. whi h a p rti ular frequ nciQirQm-the microph ne due to. basket w e. on the, r t is causedpto trip a'. .1 r her by sw t hin fl the air 'at the selectedjreduency or,rotor speed.

T o era n-ent re circuit sasfollovt h as The signal f I II I QiQ 'y 11 microrhane r ac the id ofithejelect ie'izalvejlmro shai J.- pass filt rnetwo h 28- .wf hisfil e as rve flashbpress unwanted high frequencies; the sensitivity of the va1v e 2T 20 I 11 Qd ya potentiometer ,29. ,"lfhexan d ci cuit of. he valve. :21v s tun 1;: by a a al e .rcsQnmQe. .9 :9ui .30. .,.,.ne,atpde reed resis an ei tde ounls thr a s na -W11 g Th e signal ,f-roin the .va lyegzl, ,is passed to the grid of the valve 3| through the condenser 32 and further amplified.

The signal level on the anode of the valve 3| is controlled by a diode 33 which has its cathode set at a delay voltage dependent on the setting of a potentiometer 34. When the signal level on the anode of the valve 31 exceeds the delay voltage, the diode 33 passes current which causes a voltage drop across a resistance in circuit with the cathode of the diode 33. The negative voltage produced at point 35 is passed via resistors 31 and 38, to the grid of the valve 21, thereby biasing back the grid and giving automatic gain control on this valve. This automatic gain control renders the whole amplifier tolerant to a large variation in the level of the acoustic input.

The controlled signal level at the valve 3! passes on to the electronic valve 39 via a sharply tuned band-pass filter at.

The signal on the anode of the valve 39 passes via condenser d! to the cathode of a further diode 42, the cathode being maintained at a positive potential by a tapping on potentiometer 43 taken via a relay winding 4%.

It will be appreciated that no direct current fiows through the relay winding until the signal level at the valve 39 reaches a sufficient value to back-off the positive relay voltage due to potentiometer 43. When this occurs, the relay action is sharp and rapid. Normally the relay voltage is adjusted so that the relay will operate on the sharp rising portion of the characteristic of the band-pass filter. The jet driving the rotor is controlled through relay mechanism 35, which controls a fluid valve mechanism 53 in circuit with the jet 8.

A switch button 4! is pressed to operate the rotor. This closes the battery circuit via relay winding 65 which relay controls the air supply. Only sufiicient current is passed by a resistance 50 to hold relay down after it is actuated, so that button 4'! can be pressed and then released.

The rotor will continue to accelerate until the bucket whistle resonates the amplifier and operates relay 44. This relay closes, making the battery circuit is via resistance 49 and relay winding 4&3. The relay 45 is wound in opposition to winding 45 and so cancels the field due to 45, Which allows the relay armature to drop out and so switch ff the air supply.

By adjustment of the potentiometer 34 controlling the delay voltage on the first diode, the signal level passed to the band-pass filter may be adjusted, thus selecting the frequency at which the relay M operates. This adjustment enables the machine setter to set the amplifier so that the air supply to the rotor driving jet is cut off, when the rotor reaches a speed slightly above that required to resonate the balancing frame. In this way, the time lost by the operator in waiting for the rotor speed to resonate the frame may be reduced to a few seconds.

We claim:

1. A method of dynamically balancing a rotor which comprises applying the following procedures in succession to parallel planes of the rotor which are transverse to its axis of rotation: selecting two orthogonal diameters on said plane; balancing the rotor about the first of said diameters by applying a mass first to one point on the second of said diameters and then to another point on that diameter on the opposite side of the axis of rotation of said rotor and at the same distance therefrom as the first point, rotating said rotor after each application of said mass, and measuring the out-of-balance forces during each period of rotation for each application of mass, and thus ascertaining the heavier side, removing material from any point on the heavier side oiflsaid plane until the measured out-ofbalance forces for said oppositely applied masses are the same; and balancing the rotor about the second of said diameters by repeating the operations with increments placed on the first named diameter, but in this case removing the material from a point lying on said first nameddiameter.

2. A method of dynamically balancing a rotor which comprises applying the following procedures in succession to parallel planes of the rotor which are transverse to its aXis of rotation: applying a temporary adherent mass successively to two points on a line at right angles to a diameter passing through a third point and at equal distances from said diameter, measuring the out-of-balance forces during rotation after each application, adjusting the mass of the rotor itself on said line until the out-of-balance forces in each case are equal; applying'a: temporary adherent mass successively to said third point and to a fourth point, said third and fourth points being on said diameter at equal distances from the axis of rotation, measuring the out-ofbalance forces during rotation in each case, and adjusting the mass of the rotor itself by the addition or removal of mass on said diameter until the out-of-balance forces in each case are equal.

3. An apparatus for balancing a rotor according to the method described, which comprises, in combination, a support, a frame, bearings in said frame rotatably supporting said rotor, means for resiliently mounting said frame in said support so as to be movable in a direction transverse to the rotor axis, driving means for rotatingsaid rotor at varying speeds, speed responsive means for cutting off the driving means for the rotor when the rotor speed exceeds the speed corresponding to resonance of the frame, a magnetic pick-up adapted to be operated by the vibration of said frame, and means for measuring the amplitude of the electrical vibrations generated by said pick-up. v

4. An apparatus for balancing a rotor according to the method described, which comprises, in combination, a support, a frame, bearings in said frame rotatably supporting said rotor, means for resiliently mounting said frame in said support so as to be movable in a direction transverse to the rotor axis, driving means for rotating said rotor at varying speeds, speed responsive means for cutting off the driving means for the rotor when the rotor speed exceeds the speed corresponding to resonance of the frame, a magnetic pick-up adapted to be operated by the vibration of said frame, means for measuring the amplitude of the electrical vibrations generated by said pick-up, and filters in said pick-up circuit to filter out unwanted vibrations. e

5. An apparatus for balancing a rotor according to the method described, which comprises, in combination, a support, a frame, bearings in said frame rotatably supporting said rotor, means for resiliently mounting said frame in said support so as to be movable in a direction transverse to the rotor axis, driving means for rotating said rotor at speeds up to and slightly .beyond the speed corresponding to the natural period of vibration of the resiliently mounted oscillating frame, a microphone responsive to the sound vibrations set up by the driving means at said speed, an electrical circuit containing said microphone, a band-pass filter in said circuit sharply tuned to'said vibrations corresponding to. the. frame resonance, a source. of. current.- sup.- Dly .for the rotor. driyinglmeans; a relay. insaid circuit adapted to contioLsaidsuppIy to the .120? tondrivings means, meansproviding. relay volt- :age :sunh that'the relay operates. on. the sharply rising. portion. oizthe characteristicsof thebandnassfilter, whereby the current supply .for, the .mtor. is cut off.v at. .a.-spee d corresponding tothe .nesonancaoithe frame.

.6. A method. of dynam cally balancing a rotor which comprises applyin the. followin proedures n succession to each or two parallel planes of t e, rotor which. are. transverse :to the axislofl rotation: temporarilyadjusting the mass otthe, rotor, in the given. plane. at" anarblt-raly point, rotatingthe. rotor, in. a frame. ad p edr o me sure. the. enact-balance forces and. noting said. outeofrbalance force, temporarily. adjusting the massef the rotoroe imilar extent ate point-unequal distance on..t.h diametrica ly op- ROSite ide he s in a is to. the first po n similarly rotatingthe-rotor in said :f-rame as in he-first. step nd. n ting said. ted-balanc force, permanentl adju tin e. mas of. he rotor,, on :a line.. j0ining said. two points so -that snccess-iveisim lar temp y di stmentsat said pointsm esultoinlequal. outrof-balaneef rces; an repeating thi pr c d on a line mal: to thmfi-rst .said line and passingthroughthe spin Aim thodmf dynam ca ly-ba nc n a. otor whi h. comprises app yin he.;fol w. hs. ro e: duresiimsuccession to each of two parallel planes otthe-rotor. wh ch a e trans rse to th axi of 13114118 of; vibration, permanently iadjusting the mass. of the rotor on a line joiningi lsaid two 7 so that successive temporary sirnilarad- 'iu hneht at; a d Point n equal mp itudes r vibration at Y resonance speeds; f and re- .peatihgihis. procedure on .9. line-normaL to the first saiddine and passing through the .spin. axis.

A method of {dynamically balancing a rotor according to claim 2, in which the rotor .is so rotatahly mounted that it .is .resiliently moyahle in.,djregtion,tran sverse to the rotor. axis and, .aflgerjtlrr-z. application. of the temporary mass to each oi ,said four points. rotating the motor. to a i en. nse .e d ng: a pe d er-r sponding .to the matural period of vibration of the resilient mounting of the rotorgar rd inl which .th e me asuring of the 'out-o'ff-balance L forces .ineludes" measuring the maximum amplitude of lvibration after .the application of. the. temporary mass to:-fthe. two points and inlwhich the adjusting-of grill-1e -.nia s s of the rotorIat one. of I eid.:.pe. t so effected as t u li e i 9 W maximum amplitudes a of vibration, -.and;. 1ikevyise e s ring; the )maX uml m ltude. f ib ati n aatternsuccessive applications of the temporary .mass ctotheathird v.and. fourth.;poin.ts and altering theamount of material oflthe rotonatlone of ithose poi'ntsto equalize the maximum amplie 'tudesofwibration.

9.cA method of dynamically.Joalancingamotor according-to 1c1aim.2', in..nwhich,;said Tutor isi 8 so rotatably mounted; that it: oscillatetabeut an. axis at right. angles. to thatp the rotorsh ii passing through one of: said: planes. and, after the. application of the. tempo a y mass. to eeth orsaid: four pointsmta in th -reto o st tch range of speed, includin a. spee corre pondin tozthe naturalrperied of-vihr tioh. efithere llient mcuntin -efthe e qn, andtin wh ch themee hrns/of: the out-of-balanc or e inc udes measurin the. maximum. amp itude of, vib eil h. a er thezapp cation orthe, temporary. mass .1 9: heaiirst two poin s and: wh ch the ad ustin of. the mass ofythe otor at one of aid nolnts s o effect-ed s to. equaliz the tw ample ese b tion, a lihe sewmsasur ha t ax m a p de vibratiqhlaiter sue eese sive applications of the. temporary n ass totthe h dian eu h e n sand lterihsflt anie.u of material of-.the rotor at; oneof; those. points tee uali e t aximum-amplitudes of- UPI-Q.- tion,

10. A method of dynamically.iloalancingra. rotor which. comprises. applying the; following procedures. insuccession to v each. ofv two parallel planes. ofathenotor which .are transverse to.;the axisv of :rotation: temporarily adjusting; the-mass ;oi;.t he rotor in the, given .-plane at an arbitrary point lying tonn -sided adiameter, rotating the rotor-ina-frame-adapted tomeasureithelout- :ofrbaiance'forcesand:notingsaidzquteofebalanee for0 emporarilyadiustingmhe mass. ottherotor t.o;a similar extent ata. second pQint-whichlies on a, line normal tQsaidrdiameLGr .andpassing through the first point, the second point-bein at the same d stance-from said diameterra ithe rst; poi t imi rly; rotatin :themotor in i said ram i sinth ifir tiste and notin said;out=ofha ene s er e, rmanentlyadjustin -the mass of he ratchet :a rpoint..;not .-on,;sai d=diameter s0 at ue essives milar.temmraryadiustments at the, first andsecend points-result meoualloutia an e. force and r heatin reeedure b empo a i y ahiustlns the. ass at ipo nt .on saiddiameter .at: equal ;dis t ances.;f;rom the; spin is" and ubse u nt y; ermanen diustln th m ss a poi t .01 saiddiamet r- 11. An-apparatusz er-balahcinsla retenaccssding to the method described which, copprises in em in ti h. asuppo t, .aif ama beerlngs in; said .rramelus n h sa dz ietet e ates anlaxis ubs a ia ly r en icul r to said; u ort-tw ubstant lly mi d;- to ree -i is :merem h about a ihsleex transver eo th said rocking axis being substantiall Plac sene en aieees f. P th ter ean mt et re swine; hees s e esee i pie in on isd byr he ibretie e tl eid frame b i tse si iel andmeessppet relyrse nected 411L581 i l tus se easles. ie islse eds aiat is sil eet el es s ssdt etetlbhe tse s etch WREQ TR. BEQ EEQE E 10 REFERENCES CITED Number Name Date The following references are of record in the 3 i' file of this patent: e s et a] 5' 3 2,243,458 Esval et a1 May 27, 1941 UNITED STATES PATENTS I 5 2,289,074 Rushing et a1, July 7, 1942 Number Name Date 2,348,922 Pekar May 16, 1944 710,148 Hodgkinson Sept. 30, 1902 OTHER REFERENCES gaff i f Vibration Problems in Engineering, by S. 1 009'323 E 1911 m Timoshenko, second printing, pgs. 38 through 41. 1'490109 Hort 1924 Published by D. Van Nostrand Co., Inc., 250 1:547487 111111111111; J 1925 Fourth Ave., New York, N. Y. (A copy is in 1,557,268 Newkirk Oct. 13, 1925 1,678,888 Trumpler July 31, 1928 

